ALG8 is a multipass endoplasmic reticulum membrane glucosyltransferase that builds the lipid-linked precursor for protein N-linked glycosylation. On the lumenal side of the membrane it transfers an alpha-1,3-linked glucose from dolichyl-phosphate-glucose to Glc1Man9GlcNAc2-PP-dolichol, producing the diglucosylated intermediate used by ALG10. This is the second of the three glucose additions in precursor assembly. Biallelic loss-of-function variants cause ALG8 congenital disorder of glycosylation, with defective lipid-linked oligosaccharide assembly and protein hypoglycosylation. Heterozygous loss-of-function variants are associated with polycystic liver disease, sometimes with kidney cysts.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005789 endoplasmic reticulum membrane | IBA GO_REF:0000033 | ACCEPT | Summary: The inherited ER membrane location agrees with ALG8 precursor synthesis. Reason: ALG8 uses membrane-bound donor and acceptor in the ER. UniProt curates the ER membrane location and predicts multiple membrane spans. The broader organelle-membrane assertion retains its appropriate source resolution; the separate lumenal-side annotation specifies where catalysis occurs. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000275691 UNRESOLVED The PAINT ancestral node is preserved from the source. Its complete IBD/tree placement was not independently reconstructed. Human target evidence supports the inherited assertion; neither donor count nor target self-evidence is treated as a failure. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane file:human/ALG8/ALG8-uniprot.txt In the lumen of the endoplasmic reticulum, CC adds the second glucose residue from dolichyl phosphate glucose file:human/ALG8/ALG8-uniprot.txt Multi-pass membrane protein |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: ALG8 catalyzes a glucose-addition step in lipid-linked oligosaccharide synthesis. Reason: Human patient-cell substrate accumulation and complementation support this process independently of PAINT. The product itself performs the glycosyl-transfer step, rather than merely being required as a substrate. No target-specific loss of the ancestral biosynthetic role is indicated. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000275691 UNRESOLVED The PAINT ancestral node is preserved from the source. Its complete IBD/tree placement was not independently reconstructed. Human target evidence supports the inherited assertion; neither donor count nor target self-evidence is treated as a failure. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt adds the second glucose residue from dolichyl phosphate glucose PMID:12480927 suggesting inefficient addition of the second glucose residue onto lipid-linked oligosaccharide PMID:12480927 cells from the patient were successfully complemented with wild type hALG8 cDNA |
| GO:0042283 dolichyl pyrophosphate Glc1Man9GlcNAc2 alpha-1,3-glucosyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: The PAINT molecular function matches ALG8 donor and acceptor specificity. Reason: The specific term names the second glucosylation step. Human loss-of-function and rescue evidence, together with the curated reaction, supports retaining this ancestral activity on human ALG8. This does not imply that every ALG6/ALG8-family member has the same acceptor. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000275692 UNRESOLVED The PAINT ancestral node is preserved from the source. Its complete IBD/tree placement was not independently reconstructed. Human target evidence supports the inherited assertion; neither donor count nor target self-evidence is treated as a failure. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt adds the second glucose residue from dolichyl phosphate glucose PMID:12480927 suggesting inefficient addition of the second glucose residue onto lipid-linked oligosaccharide |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: The UniProt location mapping correctly places ALG8 in the ER membrane. Reason: The mapping preserves the curated compartment. Its source uses curator inference for ER membrane location and sequence analysis for multipass topology; it is not being recast as direct imaging of endogenous human ALG8. Propagation Review Root cause: NO FAILURE CORE Sources checked: UniProtKB-SubCell:SL-0097 SUPPORTS TRANSFER The source maps the curated ER membrane location without adding finer topology. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0016758 hexosyltransferase activity | IEA GO_REF:0000002 | MODIFY | Summary: The family-level hexosyltransferase assignment can be refined for human ALG8. Reason: IPR004856 identifies the ALG6/ALG8 glucosyltransferase family. The broad activity is true; human ALG8 reaction evidence resolves the more informative Glc1Man9GlcNAc2 acceptor-specific activity. This target-level refinement does not diagnose an erroneous family assignment. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: InterPro:IPR004856 SUPPORTS TRANSFER The family supports the broad hexosyltransferase assertion. Human reaction evidence justifies a more specific target annotation, without changing the family scope. Proposed replacements: dolichyl pyrophosphate Glc1Man9GlcNAc2 alpha-1,3-glucosyltransferase activity Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt adds the second glucose residue from dolichyl phosphate glucose file:human/ALG8/ALG8-uniprot.txt Belongs to the ALG6/ALG8 glucosyltransferase family. |
| GO:0042283 dolichyl pyrophosphate Glc1Man9GlcNAc2 alpha-1,3-glucosyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: The EC/Rhea mapping captures the specific ALG8 glucosyl-transfer reaction. Reason: EC 2.4.1.265 and RHEA:31307 in the source record describe the Dol-P-Glc-dependent addition of the second glucose. These independently match the target molecular function and the human genetic experiments. Propagation Review Root cause: NO FAILURE CORE Sources checked: RHEA:31307 SUPPORTS TRANSFER The source reaction and EC 2.4.1.265 in UniProt specify the same donor, acceptor and product as the target activity. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt adds the second glucose residue from dolichyl phosphate glucose PMID:12480927 suggesting inefficient addition of the second glucose residue onto lipid-linked oligosaccharide |
| GO:0005515 protein binding | IPI PMID:25910212 Widespread macromolecular interaction perturbations in human... | REMOVE | Summary: The curated CREB3 interaction does not specify an informative ALG8 molecular function. Reason: The source is a human interaction-perturbation study, and the UniProt/IntAct record identifies the ALG8–CREB3 isoform-2 pair. Remove the generic protein-binding annotation because it does not convey a specific functional activity. This judgment neither rejects the interaction nor assigns it a signaling or adaptor role; the cached body omits the pair-level experimental results. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt Q9BVK2; O43889-2: CREB3; NbExp=3; IntAct=EBI-3921603, EBI-625022; |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | REMOVE | Summary: HuRI reports ALG8 binary interactions without resolving a distinct molecular function. Reason: The primary source describes repeated yeast two-hybrid screens and pairwise retesting; curated ALG8 partners are recorded in UniProt/IntAct. These interactions are retained as evidence, but generic protein binding adds no informative activity. No specific regulatory or scaffolding mechanism is established by the pair list. Supporting Evidence: PMID:32296183 followed by pairwise verification by quadruplicate retesting and sequence confirmation file:human/ALG8/ALG8-uniprot.txt Q9BVK2; P00387: CYB5R3; NbExp=3; IntAct=EBI-3921603, EBI-1046040; |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | REMOVE | Summary: BioPlex associates ALG8 with the preceding glucosyltransferase ALG6. Reason: Affinity-purification mass spectrometry supports a curated association between two enzymes in the same pathway. Generic protein binding does not identify a distinct ALG8 activity, so remove that uninformative term while preserving the association. Copurification alone does not establish a substrate-channeling complex or an adaptor function. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt Q9BVK2; Q9Y672: ALG6; NbExp=2; IntAct=EBI-3921603, EBI-11337956; PMID:33961781 Through affinity-purification mass spectrometry, we have created two proteome-scale, cell-line-specific interaction networks |
| GO:0006487 protein N-linked glycosylation | IEA GO_REF:0000107 | ACCEPT | Summary: The orthology transfer agrees with ALG8 participation in N-linked glycosylation. Reason: ALG8 catalyzes synthesis of the glycan precursor used for N-linked glycosylation. GO:0006488 is part of GO:0006487, and human patient experiments support the broader process. Mouse Q6P8H8 identity is verified; the exact Ensembl transfer seed is not reconstructed, so its provenance remains bounded. Propagation Review Root cause: NO FAILURE CORE Sources checked: UniProtKB:Q6P8H8 UNRESOLVED Mouse Alg8 identity is verified by UniProt/MGI. Current mouse process evidence is compatible with human data, but the exact historical transferred assertion was not reconstructed; no circularity or donor error is alleged. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt adds the second glucose residue from dolichyl phosphate glucose PMID:12480927 cells from the patient were successfully complemented with wild type hALG8 cDNA file:human/ALG8/ALG8-uniprot.txt the glycan precursors employed in CC protein asparagine (N)-glycosylation |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | TAS Reactome:R-HSA-446193 | ACCEPT | Summary: The Reactome pathway places ALG8 in lipid-linked precursor biosynthesis. Reason: The pathway includes the specific ALG8 glucose-addition reaction R-HSA-446189. This is direct catalytic participation in precursor synthesis. The parent summary contains a terminal-sugar wording error; the correct three terminal glucoses are specified by the individual reaction and UniProt. Supporting Evidence: Reactome:R-HSA-446189 The second glucose (supplied from the donor dolichol-phosphate-glucose) is added to the N-glycan precursor, mediated by ALG8 |
| GO:0098553 lumenal side of endoplasmic reticulum membrane | IC PMID:15235028 Clinical and molecular features of three patients with conge... | ACCEPT | Summary: The lumenal-side IC annotation correctly describes the catalytic face. Reason: The cited study uses topology predictions in its Discussion, rather than an endogenous localization assay. Its genetic results and the established lumenal LLO reaction support the curator inference. GO:0098553 includes proteins embedded in the lumen-facing leaflet, so it is compatible with a multipass enzyme. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt In the lumen of the endoplasmic reticulum, CC adds the second glucose residue from dolichyl phosphate glucose |
| GO:0005789 endoplasmic reticulum membrane | IGI PMID:15235028 Clinical and molecular features of three patients with conge... | ACCEPT | Summary: Human ALG8 complements the yeast ER glycosylation defect. Reason: Figure 4 tests human constructs in yeast alg8-deficient strains. Functional complementation supports the ER membrane assignment; it is not direct imaging in human tissue. The accepted IGI retains the genetic and heterologous-host scope. The external Results excerpt, canonical DOI/PMC identity and actual retrieval route are recorded in ALG8-notes.md; the local PMID cache remains bibliographic-only. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0006487 protein N-linked glycosylation | IMP PMID:15235028 Clinical and molecular features of three patients with conge... | ACCEPT | Summary: Human ALG8 deficiency impairs N-linked glycosylation. Reason: Patient glycoprotein profiles and human-construct complementation of yeast CPY glycosylation support this process. ALG8 contributes its precursor-synthesis reaction, while oligosaccharyltransferase performs glycan transfer to protein. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt adds the second glucose residue from dolichyl phosphate glucose |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IMP PMID:12480927 A deficiency in dolichyl-P-glucose:Glc1Man9GlcNAc2-PP-dolich... | ACCEPT | Summary: Patient-cell glycan profiling and rescue establish ALG8 involvement in precursor assembly. Reason: The abstract reports Glc1Man9GlcNAc2-PP-dolichol accumulation after glucosidase inhibition and rescue by wild-type human cDNA. Together with the specific glucose-transfer reaction, these experiments support direct participation in LLO biosynthesis. Supporting Evidence: PMID:12480927 suggesting inefficient addition of the second glucose residue onto lipid-linked oligosaccharide PMID:12480927 cells from the patient were successfully complemented with wild type hALG8 cDNA |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IMP PMID:15235028 Clinical and molecular features of three patients with conge... | ACCEPT | Summary: The second patient study corroborates the ALG8 precursor-synthesis step. Reason: Patient fibroblast LLO profiles and human wild-type versus mutant complementation support the specific precursor-assembly role. The data are interpreted as genetic and glycan-profile evidence. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt adds the second glucose residue from dolichyl phosphate glucose |
| GO:0042283 dolichyl pyrophosphate Glc1Man9GlcNAc2 alpha-1,3-glucosyltransferase activity | IMP PMID:12480927 A deficiency in dolichyl-P-glucose:Glc1Man9GlcNAc2-PP-dolich... | ACCEPT | Summary: Human genetic rescue supports the second-glucose transfer activity. Reason: The source connects the accumulation of the immediate glucosylated precursor with defective human ALG8 and successful wild-type rescue. This supports the curated IMP activity assignment without describing it as a purified-enzyme kinetic assay. Supporting Evidence: PMID:12480927 suggesting inefficient addition of the second glucose residue onto lipid-linked oligosaccharide PMID:12480927 cells from the patient were successfully complemented with wild type hALG8 cDNA file:human/ALG8/ALG8-uniprot.txt adds the second glucose residue from dolichyl phosphate glucose |
| GO:0042283 dolichyl pyrophosphate Glc1Man9GlcNAc2 alpha-1,3-glucosyltransferase activity | IMP PMID:15235028 Clinical and molecular features of three patients with conge... | ACCEPT | Summary: Human T47P/G275D ALG8 complementation supports the specific glucosyltransferase function. Reason: Figure 4 measures yeast growth and CPY glycosylation after expression of human wild-type or T47P/G275D constructs. The Discussion describes the assays as nonquantitative. Retain the IMP assignment without claiming direct measurement of isolated enzyme turnover. The external Results excerpt and source provenance are recorded in ALG8-notes.md; the local PMID cache remains bibliographic-only. UniProt independently records decreased activity for both variants, with the same primary citation. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt adds the second glucose residue from dolichyl phosphate glucose file:human/ALG8/ALG8-uniprot.txt decreased dolichyl pyrophosphate FT Glc1Man9GlcNAc2 alpha-1,3-glucosyltransferase activity |
| GO:0004583 dolichyl-phosphate-glucose-glycolipid alpha-glucosyltransferase activity | TAS Reactome:R-HSA-446189 | MODIFY | Summary: The normal Reactome reaction resolves the acceptor-specific ALG8 activity. Reason: The cited event explicitly assigns addition of the second glucose from Dol-P-Glc to ALG8. Refine the valid donor-specific parent to GO:0042283, which also specifies the glycan acceptor. Proposed replacements: dolichyl pyrophosphate Glc1Man9GlcNAc2 alpha-1,3-glucosyltransferase activity Supporting Evidence: Reactome:R-HSA-446189 The second glucose (supplied from the donor dolichol-phosphate-glucose) is added to the N-glycan precursor, mediated by ALG8 |
| GO:0004583 dolichyl-phosphate-glucose-glycolipid alpha-glucosyltransferase activity | TAS Reactome:R-HSA-4724330 | MODIFY | Summary: The disease event describes failure of the normal ALG8 glucosyl-transfer step. Reason: The Reactome summary states the normal reaction before describing activity-lowering disease variants. The gene-level molecular function can therefore be refined to GO:0042283. This does not assign wild-type catalytic capacity to the defective variants represented in the event. Proposed replacements: dolichyl pyrophosphate Glc1Man9GlcNAc2 alpha-1,3-glucosyltransferase activity Supporting Evidence: Reactome:R-HSA-4724330 normally adds the second glucose moiety to the lipid-linked oligosaccharide precursor (LLO aka N-glycan precursor) which is required for subsequent N-glycosylation of proteins |
| GO:0006487 protein N-linked glycosylation | ISS GO_REF:0000024 | ACCEPT | Summary: The mouse-based inference is consistent with the human glycosylation process. Reason: Human ALG8 catalyzes a precursor-synthesis step and has direct patient-cell support. The donor Q6P8H8 is mouse Alg8; its current primary glycosylation evidence includes mouse epithelial-cell work, but the exact original ISS transfer chain was not reconstructed. This limit does not contradict the supported human process. Propagation Review Root cause: NO FAILURE CORE Sources checked: UniProtKB:Q6P8H8 UNRESOLVED Mouse Alg8 identity is verified by UniProt/MGI. Current mouse process evidence is compatible with human data, but the exact historical transferred assertion was not reconstructed; no circularity or donor error is alleged. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt adds the second glucose residue from dolichyl phosphate glucose PMID:12480927 cells from the patient were successfully complemented with wild type hALG8 cDNA file:human/ALG8/ALG8-uniprot.txt the glycan precursors employed in CC protein asparagine (N)-glycosylation |
| GO:0005789 endoplasmic reticulum membrane | TAS Reactome:R-HSA-4724330 | ACCEPT | Summary: The disease-associated ALG8 entity is assigned to the ER membrane. Reason: Reactome places defective ALG8 in the compartment of the normal enzyme. Retain the broad location, which agrees with curated human ER membrane localization; this is neither a claim of restored mutant catalysis nor a higher-resolution localization experiment. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005789 endoplasmic reticulum membrane | TAS Reactome:R-HSA-446189 | ACCEPT | Summary: The normal ALG8 reaction occurs at the ER membrane. Reason: The Reactome event describes the membrane-linked precursor and donor at the ER. This agrees with the curated compartment and the lumenal catalytic face; the broader membrane term remains a valid source assertion. Supporting Evidence: file:human/ALG8/ALG8-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane file:human/ALG8/ALG8-uniprot.txt In the lumen of the endoplasmic reticulum, CC adds the second glucose residue from dolichyl phosphate glucose |
| GO:0006487 protein N-linked glycosylation | IMP PMID:12480927 A deficiency in dolichyl-P-glucose:Glc1Man9GlcNAc2-PP-dolich... | ACCEPT | Summary: ALG8 supplies a catalytic precursor-assembly step to protein N-linked glycosylation. Reason: The human deficiency study reports abnormal LLO synthesis and rescue by wild-type ALG8 cDNA. This evidence supports the broader process because precursor biosynthesis is part of N-linked glycosylation, rather than because disease severity alone implies participation. Supporting Evidence: PMID:12480927 cells from the patient were successfully complemented with wild type hALG8 cDNA file:human/ALG8/ALG8-uniprot.txt adds the second glucose residue from dolichyl phosphate glucose |
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Q: Does the ALG6–ALG8 association promote sequential glycan transfer, or reflect colocalization without a stable functional complex?
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